During the life of the well, completion work may need to occur to allow access to hydrocarbon reservoirs at various elevations, or for other reasons. If a well has access to a hydrocarbon reservoir which creates a pressure in the wellbore, access into the wellbore above this reservoir needs to occur with the lower reservoir isolated. Some wells are under balanced, meaning that, while the completion work is ongoing, the formation pressure from the producing reservoir is not offset by a column of liquid in the wellbore. Instead, in oil or gas wells the pressure from the formation needs to be isolated positively with two shutoffs before the wellhead can be opened up so that further completion work can occur. In the past, this has been accomplished with a lubricator above the wellhead. A lubricator is a chamber with valves on top and bottom which is limited in height to about 60'-80' so that tools can be hoisted into the top of it. Using lubricators limits the length of a downhole assembly and creates delays if long strings of such equipment as perforating guns are required. Single flapper subsurface safety valve arrangements are not satisfactory since dual isolation is required before the under-balanced wellbore can be accessed through the wellhead while meeting existing regulations. In a typical installation, a pair of control lines are run from the surface into a portion of the casing for operation of a known single flapper subsurface safety valve. Such control lines are used in the present invention to operate a removable valve assembly to allow long strings of tools to be assembled in the wellbore through an open wellhead.
If dual valves are used, each must be tested. The problem in the past with a dual valve arrangement has been that once the lower valve is closed and tested, the upper valve is not exposed to well pressure and cannot be tested from below. This invention solves this problem by testing the upper valve from above.
The object of the present invention is to provide a dual shutoff system with facilities to pressure test the two shutoffs to ensure their integrity. The system employs existing control line connections and has as another of its objectives that it be removable.